Potentiometers of this kind are known in general in the art, especially so in the form of rotary potentiometers.
In general, it is difficult with potentiometers to seal the interior of the potentiometer hermetically to the outside, i.e. especially the resistor path and the slider spring. DE-PS No. 27 09 998 suggests that the actuating shaft of a trimming potentiometer be sealed by a shaft collar, on the one hand, and a chamber in the casing receiving the collar, on the other hand, being filled with grease, while the casing and the cover of the casing are sealed by a casting compound. This is expensive to produce. Moreover, the sealing function of a "grease packing" is limited in time as the grease resinifies and also oozes out of its chamber if the potentiometer is used frequently.
It is likewise generally known (cf. the earlier German patent application No. P 37 14 348.4) to seal the casing and the cover, on the one hand, and the actuating shaft and the rotary driver, on the other hand, by rubber rings. That is disadvantageous, too, because such rubber rings not only are quite expensive but also involve greater expenditure in assembly and the rubber rings have a limited service life as the rubber becomes brittle.
It is known from the applicant's earlier German patent application No. P 37 17 117.8 of May 21, 1987 to mold the slider of a linear potentiometer integrally with a guide member by injection molding, the guide member presenting part of the injection mold. This injection molding technique was applied in that case so as to obtain reproducible sliding forces between the slider and the guide member, regardless of manufacturing tolerances of the guide member.
Finally, it is known from the applicant's earlier German patent application No. P 37 17 306.5 of May 22, 1987 to apply a plastics injection molding process for making both a circuit board and a soldering lug for obtaining the contacting of circuit board conductors, the two elements mentioned being pressed against each other by rams during the casting process. The contact pressure required was exerted by the plastic material itself upon curing as the material shrinks when solidifying.